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Platter issues


ronfire
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I used to be able to make the platters but now it just wont work..

I am using Plainsman M340 clay. Roll out the clay with a slab roller and then place inside a plastic serving platter. The plastic  is sprayed with cooking oil and rubbed over evenly before the clay is placed in and worked into place with a sponge and trimmed flush with the edge. I sponge the edge smooth and run my fingernail along the bottom to make sure it does not grab over the edge.

The problem is I used to be able to get them dry without all of them cracking ( usually got 2/3 or more success rate). now all of them crack.  The edge always cracks form the outside in, the edge drys to fast. Tried to loosely cover with plastic, edge cracks. Cover with a cloth, edge cracks.  Saran the edge and still crack. Cover loosely with plastic  and a hole in the middle, now the centre shrinks and get cracks 2-3" around from the edge.   The clay on the last attempt was still wet enough after it cracked that I could almost wedge it again Have tried with my reclaimed clay but now try new clay.

I tried Rolling the clay single direction, 2 directions, fold and roll fold and roll  in several directions but still no better.

I bisque to cone 04 and glaze to 6. I don't want to get away from the cone 6 glaze as that is what all my glaze and clay is

These platters sell well when i get them to work but now I am about to give up.

Was given some Laguna cone 10 clay that worked but don't want to fire cone 10. Am going to see what happens when I fire that to cone 6.

Recommendations for other cone 6 clay or any advise would be help full

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16 minutes ago, ronfire said:

I used to be able to make the platters but now it just wont work..

I am using Plainsman M340 clay. Roll out the clay with a slab roller and then place inside a plastic serving platter. The plastic  is sprayed with cooking oil and rubbed over evenly before the clay is placed in and worked into place with a sponge and trimmed flush with the edge. I sponge the edge smooth and run my fingernail along the bottom to make sure it does not grab over the edge.

The problem is I used to be able to get them dry without all of them cracking ( usually got 2/3 or more success rate). now all of them crack.  The edge always cracks form the outside in, the edge drys to fast. Tried to loosely cover with plastic, edge cracks. Cover with a cloth, edge cracks.  Saran the edge and still crack. Cover loosely with plastic  and a hole in the middle, now the centre shrinks and get cracks 2-3" around from the edge.   The clay on the last attempt was still wet enough after it cracked that I could almost wedge it again Have tried with my reclaimed clay but now try new clay.

I tried Rolling the clay single direction, 2 directions, fold and roll fold and roll  in several directions but still no better.

I bisque to cone 04 and glaze to 6. I don't want to get away from the cone 6 glaze as that is what all my glaze and clay is

These platters sell well when i get them to work but now I am about to give up.

Was given some Laguna cone 10 clay that worked but don't want to fire cone 10. Am going to see what happens when I fire that to cone 6.

Recommendations for other cone 6 clay or any advise would be help full

Sounds like the M340 does not like the process. There are many cone six clays. Reading through It seems these are cracking before you release them from the mold. Anyway, pictures of the mold, failures etc... probably will spark some ideas here.

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Wish I had taken pictures of the cracks. It always looks like a shrinkage issue. The  rim dries faster than the centre and cracks from the edge inward.  The last attempt with the plastic and a hole in the middle the clay cracked after 4 days of slow drying and it was still wet enough to wedge after the failure. I can not get to the point of firm enough to remove from the exterior form.

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I'm thinking there are 3 possible reasons for the cracking:

1. The clay just doesn't like being worked that way. 

2. The clay is sticking to the plastic platter. Once the oil soaks into the clay, it's not going to keep it from sticking very well.

3. The oil is breaking down the clay somehow and weakening the bond between the clay particles.

Try using paper towels or something like that instead of oil and see if that works.

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do not sponge the edges.   use WD40,  not cooking oil.    do not cover the piece or try to dry it slowly.  be sure the clay is not too thick.   

i make large platters in various forms, plastic, ceramic,  metal.   i never cover the work even if there are handles applied to the edges.  the clay is less than 1/4 inches thick.   thumbnail under the very edges so it cannot catch on the plastic.   you really want the clay to dry out as soon as possible so it does not crack.   

i am sure this all sounds completely opposite of what you have been doing but  what you are doing is not working.    try this method,    if you think it does not work, look at some of my albums.   look at the first page of the post "what's on your workbench?" for successful platters.  

to see the albums, click on my avatar, go to Profile, find albums then notice there are 2 pages of them.   unfortunately, the photos are not in order chronologically.   the first image is the last one posted so to see the progress of making you need to start at the last photo and click on the left arrow to get to the last one in order.   wish i knew how to fix them.

Edited by oldlady
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When I make large shallow bowl shapes in a fiberglass bowl/mold, I crumple a sheet of newspaper thoroughly (down to a little ball several times) until it's soft and flexible and line the form with it. Yes, it leaves a slight random pattern, which I can deal with, and the piece dries very evenly. 

Invest in your local print media.

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I have  ripped newspaper in long strips, dip in water and flatten into mold then place your clay into mold. Could be catching at rim after you trim.

Free the very edge by running a fine rib or tool around it after trimming. I.e. ensure edge isn't catching

Tip them out onto a hump mold of foam at leatherhard stage.

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I'm developing a hate relationship with any mold not made out of plaster. I hate using most mold release options and it sure seems to more often than not still have some sticking. Sure its me but sick of trying to perfect it. But a lot of potters have great success so I'm sure its my process and/or impatience. I absolutely hate fussing with something for extended times. Hard to make money on something that takes a lot of fuss. Maybe consider just finding another mold. Lot's of wood hump mold options and I bet you would have less trouble with those than a plastic slump mold (if I read that right). Good luck! Don't give up, sounds like your customers like your platters.

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On 3/11/2020 at 5:22 PM, ronfire said:

The clay on the last attempt was still wet enough after it cracked that I could almost wedge it again

My last 40 boxes or so of Plainsman 370 have been quite a  bit wetter than usual. Sounds like the 340 is too. I'm wondering if the clay being wetter than you are used to has anything to do the cracking with the process you use with it. Maybe the oil is getting soaked into the clay before the clay is dry enough to release? Have you tried letting the clay dry out a bit before using it?

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I use pure mold soap from Laguna /Axner on all non plaster mold forms. On a damp sponge I spread a thin layer on plastic form (oval platters) .We do this alot and it really works well. I am so baffled by folks not using the products that are made to work well.Pure lube is made for gthis process-mold release. Works great. Mail oder some as it come sin many sizes-I have a galllon (life time supply) but a quart will work just as well.

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10 hours ago, Min said:

My last 40 boxes or so of Plainsman 370 have been quite a  bit wetter than usual. Sounds like the 340 is too. I'm wondering if the clay being wetter than you are used to has anything to do the cracking with the process you use with it. Maybe the oil is getting soaked into the clay before the clay is dry enough to release? Have you tried letting the clay dry out a bit before using it?

Weird. My last batch of 390 were on the dry side: I had to work in some reclaim to soften it when I was making large items before Christmas. I just got another batch yesterday, but I haven’t cracked into it yet.

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I'm assumoing this is a slump form not a hump form??? Slumping clay into a form so it srinks away is far less troublesome than hump forms where clay hangs up on form as it shrinks ? Which is it slump (inside) or hump form  (outside)

Dryer clay is better than soft with this.

Edited by Mark C.
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16 hours ago, ronfire said:

 

Do plaster forms work better, I could make a mould of the plate with plaster and then a plaster mould to work in.

 

Generally speaking, yes.  Plaster absorbs moisture from the clay, so it dries from the air above and the plaster below.  With non-porous moulds the clay only dries from one side.  

Give it a go, but you must use proper mould release (soft soap - I bought mine from Potterycrafts) between the plate and the plaster, or they will stick together.  Wash the finished mould with vinegar to remove ALL traces of release.  Allow mould to dry thoroughly in moving air before first use.

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13 hours ago, Callie Beller Diesel said:

Weird. My last batch of 390 were on the dry side: I had to work in some reclaim to soften it when I was making large items before Christmas. I just got another batch yesterday, but I haven’t cracked into it yet.

Be interesting to hear if your new batch of 390 wetter too. I prefer soft clay, I try and avoid buying it towards the end of the summer as it's always a bit too hard for my liking then. 

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This is new clay?

Had trouble with recycled which was "short".

How thick are you rolling?

How are you transporting sheet of clay to mold?

Are overhangs supported till trimmed?

Any drag on clay as you trim?

After rolling slab and "freeing clay from rolled surface, Cut out approx size of end clay slab required.

Support slab as much as poss. into the mold and ease towards centre or gently bump mold till clay descends into mold. Use gentle pressure towards centre of mold to complete the process.

Trim while supporting clay with other hand...no stretching.

May be in your process not the clay...just saying..unless you have been experiencing success till now....

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ronfire,  is your clay wet or dry when you start to work.  to make a large piece, it should be as dry as possible.  you mention wedging the clay well.  that sounds as though it is very wet compared to dry.

could you also try flattening your clay out by smashing it hard on a solid surface like a concrete floor.  naturally, you would let it land on something flexible so you can remove it from the floor.  

it really helps to first compress the clay.   if you slice about an inch of it off a fresh  bag of clay, bend over holding the narrow end of the slice and slap it down from over your head onto the floor.  it will stretch out long and get thinner as you do this.   do it several times until the thickness is just about half an inch and the length will still fit crossways on your slab roller.  OH !    did you mention how you roll out the clay???  i am sorry if i am assuming a slab roller and you do not have one.  

the slab roller will even out the clay into a very large piece of thinner clay.  it is very compressed and should be easy to handle if it is not too wet.  keep it dry as possible as you work.   DO NOT ADD WATER OR SPONGE THE EDGES!

the easiest way to use WD40 is as a liquid.  if you have the spray can, spray  half an inch  into a small plastic container that has a lid.  use a foam brush to spread a very thin coating over the entire metal, plastic or other form you are using as the mold.  my container is about a pint size square and i use a wood handled foam brush.  i cut a hole in the lid so the handle fits tightly in it.  half an inch of liquid lasts a long time when it is covered.

it really is a very simple process and not fussy at all.   i do nothing that is fussy or makes me handle pieces more than once or twice before glazing and firing.   

 

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The last effort was with fresh clay from the bag and was a little softer. I did manage 1 with very dry clay. I do have a slab roller that I use.

I have tried with folding the clay and several passes on the slab roller . Folding and direction change between and them then a little more for the final pass.

I have lots of reclaim clay but I understand that that is more likely to crack.  Is there anything I can add to the reclaim to reduce the cracking issue, Some of it has been sitting for some time and is growing mould.

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